1. Field of the Invention
The present invention relates to a polyamide composition that gives a molded article with excellent whiteness and surface-reflectance.
2. Description of the Related Art
Because of their low power consumption, long service life and other advantages, new light sources such as LEDs (light emitting diodes) and organic electroluminescence (EL) devices have been in increasing demand for illumination, display devices and other such applications in recent years. LEDs, in particular, have been used in a variety of applications including cellular phones and other mobile communications devices, displays, automobile instrument panels, signaling devices and other electric household appliances. Electrical and electronic products such as these have been becoming lighter, thinner and more compact in response to demands for more attractive designs, easier portability, and so forth.
As a key technique to achieve this reduction in size and weight, SMT (surface mounting technology) has become very popular and is used in many electrical and electronic products. This has markedly increased the mounting density on electronic base, and has led to reductions in size and weight that had never been achieved.
When SMT is applied, the electronic parts mounted on an electronic base are entirely subjected to heating and soldering. Therefore they must be made from a material stable at the soldering temperature (approximately 240° C.). Furthermore, lead-free solder has recently become in major use due to environmental regulations, and tin-silver alloys and the like have come into use. These lead-free solders have a higher melting point than conventional lead solder, which means that the soldering temperature is made higher (approximately 260° C.). Materials that can be used in applications such as these are limited to resins such as LCP (liquid crystal polymer), PPS (polyphenylene sulfide) and heat-resistant polyamide.
LEDs are not the exception, and also must be heat resistant enough to withstand SMT. An LED is generally constituted of a semiconductor part that emits light, a lead wire, a reflector that also serves as a housing, and a transparent sealant that seals the semiconductor part. Of these components, the reflector may be made from a variety of materials such as ceramics or heat-resistant plastics. However, productivity is a problem with ceramics, and with heat-resistant plastics the problem is a decrease in optical reflectivity caused by the color change during the injection molding process, during the thermosetting of the sealant, or under the actual environmental condition in use.
The present inventors have made several patent applications relating to materials based on semi-aromatic polyamides that are heat resistant enough to withstand SMT. For instance, Japanese Patent Application Laid-Open No. Hei7-228776 discloses a composition that has excellent heat resistance as well as excellent mechanical strength, toughness, low water absorption, chemical resistance, hot water resistance, light-weightness and moldability, comprising 100 parts by weight of a polyamide composed of a dicarboxylic acid component containing mainly terephthalic acid, and a diamine component containing mainly 1,9-nonanediamine, and 0.5 to 200 parts by weight of (i) a filler with an average particle size of 0.1 to 200 μm, selected from the group consisting of silica, silica-alumina, alumina, talc, graphite, titanium dioxide, molybdenum disulfide and polytetrafluoroethylene, or 0.5 to 200 parts by weight of (ii) a fibrous filler with an average length of 0.1 to 200 mm, selected from the group consisting of wholly aromatic polyamide fibers, glass fibers, carbon fibers and boron fibers. Japanese Patent Application Laid-Open No. 2000-204244 discloses a composition that has excellent heat resistance at humidified state, dimensional stability and surface smoothness, and which gives a molded article with an attractive surface, comprising 100 parts by weight of a polyamide composed of a dicarboxylic acid component containing mainly terephthalic acid, and a diamine component containing mainly an aliphatic alkylenediamine having 6 to 18 carbon atoms, and 0.1 to 120 parts by weight of an inorganic filler with an average particle size of 2 μm or less. In addition, Japanese Patent Application Laid-Open No. Hei3-72565 discloses a composition suitable for infrared reflow-process, comprising 100 parts by weight of a resin component containing mainly a semiaromatic polyamide which has an intrinsic viscosity of 0.5 to 3.0 dL/g and a melting point of at least 280° C. and 0.1 to 5 parts by weight of a white pigment having an averagae particle size of 0.1 to 200 μm, preferably 1 to 100 μm, such as silica, silica alumina, alumina, titanium dioxide, talc and zinc oxide.
Even with these compositions, it has been found that the properties thereof need to be further improved, and, specifically, the surface-reflectance of a molded article obtained therefrom must be improved, in view of the application for the manufacture of the above-mentioned reflectors.